Can plants think?

Plants can communicate with each other using a complex system of chemical compounds. But without a brain, can a plant think?

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There are many different varieties of plants and nearly as many ways to describe them. But aside from the occasional "beautiful," "lush" or even "prickly" adjective, have you ever attached the word "intelligent" to a plant?

Turns out, we're learning a host of new things about our foliage-minded friends. Among the biggest revelations is evidence that plants can communicate using a complex system of chemical compounds. These molecular responses allow plants a measure of self-defense by, for example, attracting predators to attack the insects munching on their fibers. These chemical signals can also alert neighboring plants to danger, be it an insect, a parasite or an environmental red flag. In some cases, a plant's chemical response can produce poison that makes a clear and present pest null and void. Further, plants that are injured emit chemicals that are the equivalent of a silent scream [source: Krulwich].

Even with all this complex communication, plants still lack brains or central nerve centers that can process and disseminate information. Without a brain, can a plant think? Not in the traditional sense. You'll never sit next to a Ficus plant in a college algebra class or while waiting for a job interview. However, some scientists believe plants do exhibit a form of alternative intelligence, including the ability to gauge consequences well into the future.

Take the European barberry plant. It's prone to attack by the tephritid fruit fly, which lays its eggs inside the barberry's berries. After the eggs hatch, the larvae survive by eating the seeds inside the berries. While this is clearly bad news for the barberry, it's also bad news for the larval fruit fly, thanks to the plant's highly developed response. As the parasite takes hold, the barberry calculates risks and recalls previous actions based on internal and external conditions.

As the fruit becomes infested with the larvae, the barberry's response depends on several factors. If the fruit has two seeds, the plant will divest itself of the fruit 75 percent of the time, an act that will cause the parasite to die. Although the plant sacrifices the fruit, it manages to save the second seed, which still has a chance to germinate and grow into the next generation of barberry. However, if the fruit only has one seed, the plant will rarely terminate the berry. Instead, it appears to recognize that the seed is compromised beyond its usefulness and that the parasite could die naturally. In short, scientists speculate that the plant anticipates both the losses and risks by either selectively terminating its own fruit in order to prevent a fruit fly infestation or allowing the fruit to continue to grow when its termination will have little effect [source: Meyer].

In addition, plants have been shown to have a sense of direction; they'll aim their roots downward to the ground, no matter how they are oriented. Some also have the ability to use camouflage by appearing to shrivel when touched and look less enticing to plant eaters [source: Newitz].